Recently, a touch detection device called a touch panel, which is capable of detecting an external proximity object, has been receiving attention. The touch panel is used for a display with a touch detection function, in which the touch panel is mounted on or integrated with a display such as a liquid crystal display. The display with a touch detection function displays various button images on the display, thereby making it possible to input information by means of the touch panel instead of by means of a conventional mechanical button. The display with a touch detection function, which has such a touch panel, does not need an input device such as a keyboard, mouse, and a keypad. For this reason, the use of the touch panel is expanding, not only in a computer, but also a portable information terminal such as a mobile phone.
There are several kinds of methods used for the touch detection device, including an optical method, a resistive method, and a capacitive method. Particularly, the touch detection device using a capacitive method has a relatively simple structure, requiring low power consumption. The touch detection device is, therefore, used for a portable information terminal, and the like. For example, capacitive touch panels are described in Japanese Patent Application Laid-Open Publication No. 2014-134900 (Patent Document 1) and Japanese Patent Application Laid-Open Publication No. 2012-047807 (Patent Document 2).